The present invention relates to adaptive circuits. More specifically, the present invention relates to an apparatus and method for controlling adaptive circuits, such as controlling gain and phase adjustments in a feed forward amplifier circuit.
Adaptive circuits are well known and used in a variety of applications. One well known example of an adaptive circuit is the feed forward amplifier (xe2x80x9cFFAxe2x80x9d). In order to achieve linearity in a feed forward amplifier, careful control of the amplifier circuitry is required. In particular, in FFA""s two or more gain and phase adjusters are often employed and the taps of each of these adjusters are carefully steered to achieve linearity through the amplifier.
Within the art of FFAs, it is known to use detector-controller circuits, one for each gain-and-phase adjuster. Each detector-controller circuit is operable to steer the taps of its respective gain-and-phase adjuster in the FFA so that the main amplifier and correctional amplifier can properly cooperate in order to reduce error introduced by the main amplifier and, should a pilot tone be used in the FFA, to also reduce the pilot tone injected prior to the main amplifier.
In certain prior art detector-controller circuits, once the detector portion of the detector-controller circuit has indicated that the associated controller circuit should make an adjustment, the controller arbitrarily steers the taps of the gain-and-phase adjuster in a direction to either increase or decrease the input to the tap, without knowing which of an increase or decrease will actually achieve the desired effect. In order to verify whether the controller steered the tap in the correct direction (e.g.xe2x80x94increased the signal to the tap), the detector circuit ascertains whether the direction of the variation brought about the desired effect, and, if so, instructs the controller circuit to continue steering in the same direction. If, however, the detector circuit ascertains that the steering direction brought about an undesired result, then the detector instructs to the controller to try steering the tap in the opposite direction (e.g.xe2x80x94decrease the signal to the tap)
In the prior art, each detector-controller circuit works independently of each other, and therefore achieving convergence towards an optimum level for each tap of each adjuster can be difficult. For example, rapid changes to the input signal being amplified by the FFA can make it difficult for the detector-controller circuits to respond quickly enough to converge the tap levels of each gain-and-phase adjuster towards the respective optimum levels. Furthermore, the adjustment of one tap of a gain-and-phase adjuster can disrupt an optimum or near optimum input level achieved at another tap, therefore cascading disruptions through all of the taps.
The inventor of the present invention also believes that a further problem is that such prior art controller circuits tend to result in taps being steered to levels that are levels corresponding to local minima for the input signal, missing a global optimum for the input signal.
It is an object of the present invention to provide a novel apparatus and method for controlling an adaptive circuit that obviates or mitigates at least one of the above-identified disadvantages of the prior art. It is a further object of the present invention to provide a novel feed forward amplifier that obviates or mitigates at least one of the above-identified disadvantages of the prior art.
In one aspect of the present invention, there is provided an adaptive circuit comprising: at least two adjusters, each adjuster including at least one control input to alter the operation of the circuit; at least one signal generator to create a tracer signal, each created tracer signal being orthogonal to each other created tracer signal; at least two controllers, each controller operable to output a control signal to at least a respective one of the control inputs of the at least two adjusters, a different orthogonal tracer signal from said at least one signal generator being applied to each respective control signal as a dither; and at least one detector operable to extract at least one orthogonal tracer signal from the circuit and to apply the extracted at least one orthogonal tracer signal to a respective one of the at least two controllers, each controller being responsive to the respective applied signal to alter the respective control signal to converge operation of the circuit to an optimal or near optimal configuration.
Preferably, the at least two adjusters operate to adjust the phase and gain of a signal passed through them and each of the at least two adjusters includes a phase control input tap to control the phase adjustment and a gain control input tap to control the gain adjustment.
Also preferably, the adaptive circuit includes at least two detectors, each of which extracts at least two orthogonal tracer signals and applies the extracted orthogonal tracer signals to a respective one of the phase control input tap and the gain control input tap of a respective adjuster.
While it is presently preferred that the orthogonal tracer signals are Walsh codes, other orthogonal, or near orthogonal, signals such as pseudo noise sequences can be employed.
According to another aspect of the present invention, there is provided a feed forward amplifier comprising: an amplifier portion including a coupler, first and second gain and phase adjusters, first and second delay elements, a main amplifier and a correctional amplifier, the coupler providing an input signal to said amplifier portion to a first signal path including the first gain and phase adjuster, the main amplifier and the first delay element and an output and the coupler providing the input signal to a second signal path including the second delay element, the second gain and phase adjuster and the correctional amplifier having a first signal path for carrying an input signal to a first gain-and-phase adjuster and a main-amplifier, said first gain-and-phase adjuster having a pair of taps for steering said first adjuster, said amplifier portion having a second signal path for carrying a sample of said input signal generated to a second gain-and-phase adjuster and a correctional-amplifier, said second gain-and-phase adjuster having a pair of taps for steering said adjuster; and a detector-controller portion having a first detector for receiving a detected signal from said first signal path and a second detector for receiving a detected signal from said second signal path, said detector-controller portion further comprising a first pair of controllers for receiving said detected signal from said first detector and a second pair of controllers for receiving said detected signal from said second detector, said controllers each operable to steer a respective one of said taps based on said received detected signals, each of said controllers further operable to inject tracer-signals into its respective tap, said tracer-signals for carrying through said amplifier portion and modulating said detected signals, said controllers each operable to extract from its respective detected signals a tap-signal by using its respective said tracer-signal, said controllers each further operable to utilize said extracted tap-signal to determine a desired direction for steering its respective tap and to output, substantially simultaneously with each other controller, a signal to steer said respective tap.
According to yet another aspect of the present invention, there is provided a feed forward amplifier comprising:
an amplifier portion including:
(a) a first signal path having a first gain and phase adjuster, a main amplifier and a delay element; and
(b) a second signal path having a delay element, a second gain and phase adjuster and a correctional amplifier, each gain and phase adjuster including a control input tap to accept an input to alter the phase response of the gain and phase adjuster and a control input tap to accept an input to alter the gain response of the gain and phase adjuster, the first and second signal paths having a common signal input and a common signal output; and
a detector portion including:
(c) a first detector to receive a signal from the common signal output and to provide the received signal to a first controller operable to create an input to the gain tap of the second gain and phase adjuster and to provide the received signal to a second controller operable to create an input to the phase tap of the second gain and phase adjuster; and
(d) a second detector to receive a signal from the second signal path before the second gain and phase adjuster and to provide the received signal to a first controller operable to create an input to the gain tap of the first gain and phase adjuster and to provide the received signal to a second controller operable to create an input to the phase tap of the first gain and phase adjuster, each controller responsive to a component in said received signals which is orthogonal to the components to which each other controller are responsive to and all the created inputs being applied to the taps substantially simultaneously and altering the operation of said feed forward amplifier to linearize the amplification of the input signal through the feed forward amplifier.
According to yet another aspect of the present invention, there is provided a method for operating an adaptive control circuit having a plurality of control input taps, said method comprising, for each said control input, the steps of: detecting a signal, including a tracer signal, from said circuit; extracting a measurement from the tracer signal in said detected signal; determining an appropriate input to be applied to said control input to improve operation of said adaptive circuit; creating a tracer signal for said control input, said created tracer signal being orthogonal to the tracer signals created for each other control input; and combining said tracer signal and said determined input and applying the resulting signal to said control input.
An apparatus and method for operating an adaptive circuit includes injecting a set of orthogonal tracer signals into the circuit. The tracers signals are extracted after modification during operation of at least a portion of the circuit and are examined by respective controllers to modify operation of the circuit.
In one embodiment, the invention is incorporated into a feed forward amplifier where a set of orthogonal tracer signals are injected into the amplifier. A detector controller detects the orthogonal tracer signals, as modified by portions of the amplifier, and applies each tracer signal to a respective controller. Each controller examines its respective signal and modifies its output to control a portion of the amplifier accordingly. The controllers apply their outputs to the respective portions of the amplifier at substantially the same time, leading to quick convergence of the operating point of the amplifier to an optimal, or near-optimal, configuration. Injection of the tracer signals into the amplifier is accomplished by dithering the controller outputs by the respective orthogonal tracer signals.